Homogeneity testing is of the highest importance for the certification of reference materials as it should demonstrate the validity of the certified values and their uncertainties for the analysis of individual units, or portions thereof.However, the conclusions drawn from the results of these studies may often be questioned.It is proposed to improve this situation by quantifying the effect of homogeneity studies in terms of their impact on certified values. Hereby, it should be noted that the betwwen-units variability directly affects the certified uncertainty, whereas the within-unit inhomogeneity only defines the minimum representative sample size.